The last month has been pretty intense, with an exhibit opening, getting our Petridish fundraising page launched, and various administrative duties. I needed to get away for a few days, so Tim and I headed off for a couple of nights at Hungry Mother State Park, near Marion, Virginia; no cell service, no internet, just peace and quiet! Of course, that didn’t mean there was no geology.
We stayed in one of the park’s cabins, built by the CCC in the 1930’s. I found the rock foundation of the cabin interesting, since it’s completely different from the Devonian shales that the cabin is built on. Instead, these are coarse-grained rocks, and many of them are cross-bedded:
About 5 miles south of the park along Highway 16 we found some old abandoned quarries. According the the Geologic Map of Virginia, these quarries are in the Cambrian Knox Group or Elbrook Formation, which are dominated by dolostones. The cabin stones, however, appear to be mostly sandstones. This doesn’t rule out the Cambrian quarries, but it makes them a less likely source. There are Silurian sandstones mapped on the north side of the park, less than a kilometer from our cabin. We didn’t see any old quarries in that area, but it’s a good possibility that was the source of the building stones.
On our second day at the park we drove north along Highway 16 toward Tazewell. Just north of the park we found large exposures of sediments:
We soon found a reasonably safe place to pull over, and the rocks turned out to be filled with brachiopods:
Again referring to the maps, this seems to be part of the Eggleston Formation, which is locally fossiliferous. While we were looking for fossils we stumbled across another interesting feature, a non-fossiliferous clay bed that ranged from about 9- to 20-cm thick:
The bed was remarkably consistent across the entire exposure, easily traced because the clay erodes back more rapidly than the surrounding rocks:
This bed is almost certainly a K-bentonite, an altered volcanic ash bed. During the Late Ordovician a subduction zone was located near what is now Virginia, and the associated volcanoes blew ash clouds far and wide. Several K-bentonite beds have been reported from the Eggleston Formation, including the Deicke and Millbrig beds that are found over huge areas and represent gigantic eruptions. I’m not sure which particular K-bentonite this represents, but it was a nice find, especially since we didn’t go there looking for it.
Not a bad way to spend a vacation!